Open hearth furnace



Aug. 8, 1939. G. w. PUTNAM OPEN HEARTH-FURNACE Filed May 21, 1958 2Sheets-Sheet l.n

Aug. 8, 1939.

G. w. PUTNAM OPEN HEARTH FURNACE 2 sheets-sheet 2 Filed May 21, 1938 efof 6,45 Po/P INVENTOR. GOEGE W PUTA/AM ATTORNEYS Patented Aug. 8, 1939UNITED STATES PATENT OFFICE OPEN HEARTH FURNACE Application May 21,1938, Serial No. 209,299

12 Claims.

This invention relates to open hearth furnaces and is particularlyconcerned with such furnaces of the regenerative type which embody newand improved features of construction and operate with high efficiencyas measured by tons of metal produced per hour and the fuel consumed insuch production.

The high eiciency of furnaces embodying the present invention isbelieved to be the result of extremely rapid and thorough mixing of thefuel and air, and control of the length, shape, direction andtemperature of the flame. These results are largely accomplished by anew and improved combination, location and arrangement of the parts ofthe port ends of the furnace including the floor, apron, roof and sidewalls thereof.

According to this invention a stream of fuel is discharged into a mixingchamber from av point high above the surface of the charge in themelting chamber and more or less horizontally and approximately kalongthe longitudinal plan center line of the furnace. The stream of fuel isso discharged into the mixing chamber that after it enters the chamberit does not contact with the walls defining that chamber, andparticularly the apron. Large volumes of air are directed downwardlyonto the top, and around and later ally into the sides, of the fuelstream, and other large volumes of air are directed from each sideunderneath the fuel stream from the time it enters the mixing chamber.A'Ihus the air completely encircles the stream of fuel from the timeitenters the mixing chamber until combustion is largely, if notentirely, completed and results in an extremely rapid mixing of air withthe fuel, especially on the under side of the fuel stream. The resultingflame is short and is much hotter on the bottom than flames from priorports with Which I am familiar.

The length of the flame may be Varied within certain limits by varyingthe amounts and pressures of gas and fuel and by varying the size,

shape and relative location of walls and floorsl Good results in theport ends of the furnace. have been obtained by regulating the length ofthe flame so that its tip is between the second and third doors of themelting chamber, i. e., with the flame extending for less than aboutonehalf of the length of the melting chamber. With such a flame thecombustion -is completed long before the outgoing gases reach theexhaust port end of the furnace, with the result that combustion doesnot continue in the exhaust port end of the furnace and the brickworktherein is not subjected to excessively high heat.

The admission of fuel and air into the mixing chamber at elevation highabove the surface of the charge in lthe melting chamber, together 5 withthe shape, arrangement and location of the Walls defining the mixingchamber, result in directing the flame downwardly into the meltingchamber to impinge on the surface of the charge therein near theadjacent end of the charge, and 10 to lie close to the charge from thepoint of rst impingement to points near the tip of the flame.

In this manner heat is transmitted to the charge by convection andradiation and a large amount is conducted directly from the iiamel tothe l5 charge. In prior furnaces wherein the flame did not impn'ge onthe charge the transfer of heat from the flame to the charge was mainlyby convection and radiation.

The shape, arrangement and location of the mixing chamber walls are suchthat the areas of the mixing chamber expand from the points of entry ofthe gas and fuel passages thereinto to the mixing chamber port, i. e.,the place where the mixing chamber opens into the melting chamber, andthe mixing chamber walls are so arranged that the originally cylindricalshape of the flame is not distorted or flattened out to an objectionableextent when it i's deflected downwardly into the melting chamber, andthe direction of the flame is held fairly close` to lines parallel tothe center line of the furnace.

Briefly stated, important results of the rapid and thorough mixing offuel and air, and particularly on the under side of the fuel stream, andthe control of the length, shape, direction and temperature of the flameare much faster melting of the'charge, much less consumption of fuel, amaterial decrease in the amount of heat carried out of the furnace bywaste gases 40 and less damage to the brickwork of the furnace. Anotherresult of major importance is that the port ends of the furnacemay berelativelyshort as compared with prior port ends and the melting chambermay be considerably lengthened all without any increase in overalllength of the furnace, and greater tonnages of steel can be produced infurnaces of this invention than in furnaces of the same overall lengthbut equipped with prior port end constructions.

In the drawings accompanying and forming a part of this specificationand in which one embodiment of the present invention is shown,

Figure 1 is a vertical, central, longitudinal, sectional view taken thruabout one-half of an open hearth furnace embodying the presentinvention: Fig. 2 is a horizontal sectional view taken on line 2-2 ofFig. 1.

Figs. 3 and. 4 are fragmentary views corresponding to portions of Figs.1 and 2 respec- Y tively;

- as "wing walls.

Figs. 5 and 6 are diagrams showing areas of the air and fuel passagesentering the mixing chamber, and the mixing chamber port respectively.

Fig. 'l is a diagrammatic view showing the manner of development of theplanes of Fig. 5.

Figs. 1 and 2 show about one-half of a regenerative type, producer gas,open hearth furnace embodying the present invention, it being understoodthat the remainder of the furnace is substantially the same as the partillustrated in these figures, and that the dot and dash lines indicatingdoors on Fig. l are not actually doors in the back wall but merelyindicate where the doors in the front wall are located.

The furnace herein illustrated is supported on the ordinary supportingstructure, and beneath the furnace are located the usual regeneratorchambers and passages leading to and from the same, the supportingstructure and regenerators not being shown. The furnace consists of twomajor parts, viz: the melting chamber I and port ends 2 at either endthereof.

The melting chamber I has a front Wall 3 provided with the usualcharging door openings 4, the lower edges of which are located on whatis known as the sill or fore plate line, indicated at 5 on Fig. 1. Theback wall 6 of the melting chamber slopes upwardly and outwardly toabout the elevation of the top of the front wall 3 and the arched roof lrests on the tops of walls 3 and 5. The ends 8 of the back wall inclinetoward the front wall 3 at the port ends of the furnace.

Each port end 2 includes an end wall, side walls, roof and bottom.- Theendwall Il! is composed of upright bulkhead parts Illa and Illb. Theside walls II and I2 unite with the end wall Il, extend forwardly,toward the melting chamber and merge into walls I3 and I4 respectivelywhich, in turn, unite with end walls I5 and I5 of the melting chamber.'I'he walls I3 and I4 have inner surfaces which extend convergingly atacute angles to the vertical plane on the center line of vthe furnace.The lwall portions I3, I4, I5 and I6 resemble, in certain respects,walls which have heretofore been known, collectively,

The roof includes a substantially horizontal, arc shaped part I1 whichex- -tends forwardly from the end wall III and a forward part Il slopingdownwardly, at a steep angle to the horizontal, to the knuckle Isa, i.e., the' junction with the roof 1, the knuckle preferably being locatedat or near the walls I5 and II. The bottom of the port end 2 includes anapron I 0 which slopes upward, uninterruptedly and at a steep angle tothe horizontal, from hearth l to its junction with the floors 20 and 2|respectively of the air and fuel passages presently to be described. Themelting chamber end walls I5 and Il, the roof Il and the apron I8 definean opening, substantially as shown in Fig. 6, between the meltingchamber and the port end 2. 'I'he melting chamber end of that opening ishereinafter referred to as the mixing chamber port. It will be notedthat the knuckle Ila is high and in fact is not much lower than theroof 1. It is possible to keep the knuckle high because most of themixing of fuel and air takes place before the gases reach the knuckle,and

the high heels of the fuel and air passages and steep roof and aprongive the desired direction to the name without requiring a low knuckle.

An arch 22, shown as an inverted substantially U-shaped wall, isdisposed within each port end 2 and rests on upright walls 23 and isunited with the end wall I0 and the bottom of the port end. This arch,together with floor 20, defines a fuel passage 24 which is approximatelyhorizontal, that is, it may incline downwardly at an angle in theneighborhood of about 10 degrees to the horizontal. The mixing chamberend of passage 24 is the fuel passage port into the mixing chamber. Thepassage .24 connects the mixing chamber with a vertical passage 25 whichin turn communicates with a regenerator (not shown) thru passage 28.

It will be understood that the wall dening the sides and top of passage24 need not be U-shaped as shown by arch 22 for this Wall may bevariously shaped to constitute the sides and top of a tunnel-likestructure for a fuel passage. The term arch-like structure is intendedto include all such tunnel forming walls.

Upright air passages 2l and 28, connected thru passage 29 to aregenerator (not shown), open at their upper ends, into an inverted,generally U-shaped air chamber on both sides, and over the top, of arch22. An air passage defined by the arch 22, floors 2l, side walls I3 andI4, roof I8 and parts of apron I9 connects that air chamber with themixing chamber. The mixing chamber end of the air passage is the airpassage port into the mixing chamber.

It will be noted, particularly by reference to Fig. 2, that the apron I9intersects with floors 20 and 2l of the fuel and air passages in asubstantially straight horizontal line extending transversely of thefurnace and located at the lower side of the inner end of the fuelpassage port, that is at the mixing chamber end of floor 2U of fuelpassage 24, and that the floors 2l are somewhat steeper and shorter thanfloor 20, but extend up to substantially the same elevation. It willalso be noted that the heels of the air and fuel passages leading to themixing chamber are on substantially the same elevation and are far abovethe surface of the charge in the melting chamber, that is, the sill orfore plate line. The heel of the fuel passage is the intersection of thefloor 2U and the upright frontwall surface defining vertical passage 25.The heel of the air passage is the intersection of the floors 2l and theupright front Walls of passages 21 and 2l.

The floors 2l of the air passages may intersect with apron I9 at a levelbelow that at which the fuel passage floor 20 intersects with apron I9if desired, for such a construction permits air to flow underneath thegas stream quite readily, but

the intersection of floors 2I,and I9 should not bematerially above theintersection of gas passage oor 20 91nd apron I9, for such anarrangement would`tend to reduce the amount of air which could flowunder the fuel stream in the mixing chamber and might also tend toretard the speed at which such air could flow under the fuel stream.

From the preceding description it will be underplanes extending from thesides of arch 20 to the inner surfaces of walls I3 and I4 atsubstantially right angles to the latter., the upper parts of whichplanes are tipped forwardly so as to intersect the roof I8 atsubstantially right angles thereto, and the parts of roof I8 and apronI9 included by said planes, walls and ports.

The location and arrangement of the roof I8, apron I9, and the innersurfaces of walls I3 and Il, are quite important. The roof I8 may slopedownwardly at an angle of between about degrees and about degrees to thehorizontal. The angularity of the apron I9 to the horizontal may varyfrom about 30 degrees to 50 degrees or more.

The terms steep and steeply as used herein with reference to apron I9and also to roof I8 are intended to include angles to the horizontalwithin the ranges just specified. The angularity of the inner surfacesof walls I3 and I4 to a vertical plane on the center line of the furnacemay Vary from about 40 degrees to about 50 degrees. The intersection ofthe inner surfaces of walls I3 and I4 with the parallel opposed surfacesof walls I5 and I6 may be located in different places with respect bothtc the knuckle and the melting chamber end of arch 22. If suchintersections are too close to the arch 22, and too far away from theknuckle the size of the air passages will be reduced and the length ofthe mixing chamber may be shortened and the mixing of air and fuel inthe mixing chamber may not be as rapid and thorough as desired and theflame may spread laterally to an undesired extent.

If those intersections are too far away from the arch 22 and too closeto the knuckles, too much air or too little air may enter the mixingchamber, depending on the air velocity, or the air may be directedlaterally toward the fuel stream at too small an angle so that the airmay not be utilized to the best advantage in rapidly making a thoroughand complete mixture of air and fuel.

It is important that the end 30 of arch 22 should be spaced far enoughaway from the under side of roof I8 to prevent premature injury to theroof and to itself by outgoing heated gases, and not so far away as topermit too much air to enter the top of the mixing chamber.

Very good results have been obtained commercially with 150 ton capacityfurnaces in which the apron I8 made an angle of about 38 degrees withthe horizontal, the fuel passage 24 made an angle of about 10 degreeswith the horizontal, the roof I8 made an angle of about 35 degrees withthe horizontal, the inner surfaces Vof walls I3 and I4 made angles toabout 50 degrees with a Vertical plane on the center line ,of thefurnace, the intersections of the inner surfaces of walls I3 and H withthe opposed parallel faces of walls I5 and I6 were located about twofeet from the melting chamber end of arch 22 and about one foot from theknuckle in the furnace roof, the front end 30 of arch 22 was about twofeet from roof I8, the heels of the fuel and air passages were aboutfour and one-half feet above the sill or fore plate line, and the apronintersected the floors of the fuel and air passages in a horizontal linedrawn across the lower edge of the fuel passage port.

In the foregoing furnaces the combined area of the air and gas passagesentering the mixing chambers was between one and two sq. ft. less thanthe 43-sq. ft. shown by Fig. 5 because the lower corners and floor ofthe fuel passagewere filled ln to make the opening more near-ly round.

The area of the mixing chamber port was about 48.3 sq. ft. (Fig. 6).Thus the mixing chamber expanded about six or seven sq. ft. or fromabout 14% to about 17% from the air and fuel passage ports to its port.

The arch 22 is slightly offset with respect to the furnace center line,as shown in Fig. 4. This offsetting results in passage 21 being slightlylarger in area than passage 28. The inner surface of wall I3 makes aslightly greater angle with wall II than wall I4 makes with its wall I2.

Figure 3 and 4 show the herein described angles of the apron, roof, sidewalls and of the fuel and air land together with Figs. 5 and 6 will makeclear how and where the areas of fuel and air passages and the area ofthe mixing chamber port are taken. The area of the latter port is takenon a plane indicated by lines 6-6 of Fig. 3.

Fig. 5 shows the cross-sectional areas of air and gas passages enteringthe mixing chamber and Fig. 6 shows the cross-sectional area of themixing chamber port. As will be noted from these figures, the area ofthe mixing chamber port is somewhat greater than the combined areas ofthe air and gas passages entering into the mixing chamber. Moreover, thecross-sectional area of the mixing chamber increases more or lessuniformly from the entering Vair and gas passages to its port, due inpart to the divergence of the roof and apron.

The area of the air passage entering the mix.- ing chamber may be morereadily determined by theoretically dividing the air passage into threeparts and adding together their individual areas. As is shown by Fig. 5,two of these parts, :c and y, are on opposite sides of arch 22, and thethird part .e lies over the arch 22 and joints the tops of parts n: andy. The area of each of these parts m, y and z, is determined bymeasuring the areas of the smallest plane disposed substantially atright angles to the direction of air flow thru each of these parts.Since the plane on which the areas of each of these parts are taken iscurved or dished and it is difficult to show such a plane in thedrawings, that plane has been shown flattened out into a, single plane,as shown in Fig. 5, wherein the parts x, y and e thereof areillustrated.

The operation of the above described furnace, particularly as regardsthe travel and action of the air and fuel, is substantially asfollowsz-A charge having been placed in melting chamber I, heated airand fuel are passed thru one port end 2, the mixture is burned inmelting chamber I and the waste gases arewithdrawn thru the oppositeport end 2. The heated fuel is directed thru fuel passages 24 across themixing chamber toward the' central part of the mixing chamber port andalong lines which are approximately horizontal. Simultaneously theheated air from passages 21 and 28 is directed into the mixing chamber.The roof I8 directs air down onto the top and along the sides of thefuel stream. The inner surfaces of walls I3 and I4 direct air laterallyinto opposite sides of the fuel stream. These surfaces and the roofdirect air under the fuel stream in the space between that stream andapron I9. 'I'he air, which is traveling at a high velocity due partly tothe high ports, thus begins to mix with the fuel on all sides of thefuel stream at the instant the stream enters the mixing chamber andalmost instantly makes a goed combustible mixture particularly on theentire lower side of the stream of fuel.

and sidesof the stream of fuel and directs it,

At the same time "the air mixes thoroughly and rapidly with the top andthe flame, downwardly thru the lower part of the mixing chamber portinto the melting chamber where the very hot, largely undistorted flameimpinges directly against the adjacent end of the top surface of thecharge.

The part of the flame between its top and the place of such impingementlies close to the charge. The waste gases have to rise steeply to enterthe exhaust port and hence are not able to carry with them as much slagand other solids as is the case with low port furnaces and thus thedeposition of such materials in the ports and checkers is retarded andreduced.

Altho the hereinabove specifically described furnace is a producer gasfurnace, the principles of the present invention may be employedadvantageously in furnaces operating on natural gas, coke oven gas,mixed gases, oil, combination and other fuels, with such variations inthe construction of the end ports as the nature of the fuel used maynecessitate.

Producer gas furnaces embodying the present invention and having anoverall length of about 70 feet have been operated commercially in twodifferent plants and have consistently produced over 121/2 tons of steelper hour with a fuel consumption of about 3,600,000 B. t. usu per ton.The best that could be done with other furnaces ln the same plants andunder comparable conditions, except that the furnaces were equipped withthe prior ports, was about 111/2 tons per hour and a fuel consumption ofover 4,400,000 B. t. u's.

It will be understood that this invention may be used to good advantageon furnaces having either long or short hearths and that on Shortfurnaces its advantages are even more pronounced than on longerfurnaces.

Having thus described the present invention so that those skilled in theart may be able to understand and practice the same I state that what Idesire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

l. An open hearth furnace including a melting chamber and mixingchambers at each end of said melting chamber, each mixing chamber havingfuel and air passages opening thereinto thru ports and having a portopening therefrom into the melting chamber, each mixing chamber having.a steep apron sloping down uninterruptedly from the lower side of saidfuel passage port, the included angle between said apron and aprojection of said fuel passage into the mixing chamber being greaterthan about 20.

2. An open hearth furnace including a melting chamber and mixingchambers at each end thereof, each mixing chamber having fuel and airpassages opening thereinto thru ports and having a port openingtherefrom into the melting chamber each mixing chamber having a steepapron sloping down uninterruptedly from the lower side of said airpassage port, and making with the horizontal an included angle ofbetween about and about 50.

3. An open hearth, regenerative type furnace including a meltingchamber, mixing chambers at each end thereof, each mixing chamber havinga fuel passage defined in part by a floor and opening thereinto thru anarch-like structure, an air passage opening into the mixing chamber onthe sides and top of said arch-like structure, a`

port opening from each mixing chamber into the melting chamber, a rooffor each mixing chamber spaced a considerable distance above saidarch-like structure, and sloping down toward said said mixing chamberhaving a roof sloping down toward said melting chamber and an apronsloping down uninterruptedly and steeply from its junction with thefloors of the fuel passage to the melting chamber and making an includedangle with the horizontal approximating that made by said roof andgreater than that made by said fuel passage floor, and opposite sidewalls extending convergingly toward the mixing chamber at acute anglesto the center vertical plane of the furnace to direct air laterally intothe mixing chamber against the sides of and underneath a stream of fuelissuing from said fuel passage.

5. An open hearth regenerative type furnace including a melting chamberYmixing chambers at each end of and communicating with said meltingchamber, each mixing chamber having fuel and air passages openingthereinto thru ports, each mixing chamber having a downwardly slopingsteep roof, an apron sloping down uninterruptedly and steeply from thelower side of said fuel passage port at an included angle to thehorizontal of between about 30 and about 50, and side walls extendingconvergingly toward the mixing chamber at different acute angles to thecenter vertical plane of the furnace,

6. An open hearth, regenerative type furnace including a meltingchamber, mixing chambers at each end of and communicating tiierewith,air and fuel passages at each end of the furnace having heels disposedrelatively high above the top of a charge in the melting chamber andhaving floors sloping downwardly from said heels toward said mixingchamber said passages opening into the mixing chamber, said fuel passagebeing defined in part by an arch-like structure, a roof for each mixingchamber sloping downwardly toward the melting chamber at an includedangle to the horizontal of between about 30 and about 40, an apronsloping down uninterruptedly from the mixing chamber ends of saidpassages to the melting chamber at a steep included angle to thehorizontal of between about 30 and about 50 and greater than theincluded angle of said roof to said horizontal, said roof and arch-likestructure being spaced apart sufliciently to prevent injury thereto byheated outgoing gases, and side walls partially defining the air passageand extending convergingly toward the mixing chamber at acute angles tothe center line of the furnace.

7. An open hearth, regenerative type furnace including a meltingchamber, a mixing chamber, an arch-like structure defining in part a'fuel passage positioned to direct an approximately horizontal stream offuel into the mixing chamber and out of contact with the walls thereof,an apron in said mixing chamber sloping down uninterruptedly from thebottom of the mixing chamber end of said fuel passage at an includedangle to the fuel stream of between about 20 and about 40, a downwardlysloping roof for said mixing chamber making an included angle with saidfuel stream of between about 20 and about 30 and spaced far enough fromsaid arch-like structure to prevent premature injury to itself byoutgoing gases, and inwardly projecting opposed walls extending upwardlyfrom the apron at the belting chamber end of said mixing chamber.

8. An open hearth furnace including a melting chamber and port endsopening thereinto at the ends thereof, each port end including anarchlike structure and floor defining a fuel passage extendingdownwardly at a small included angle to the horizontal toward themelting chamber, en'd and side walls and a horizontal arched roofdefining an air chamber on the sides of and above said arch-likestructure, a steep roof sloping down at a large obtuse angle from saidhorizontal roof,

a relatively high knuckle, a steep apron sloping down at an includedangle between about and about to the horizontal from the bottom of iemelting chamber end of the fuel passage to the hearth of the meltingchamber, and opposed side walls having inner surfaces inclined at anacute angle to the vertical center plane of the furnace and terminatingbetween the vertical plane of the knuckle and the melting chamber end ofsaid arch-like structure and nearer to the former than to the latter.

9. An open hearth furnace comprising a melting chamber having asubstantially horizontal roof, knuckles close to the elevation of saidroof, and port ends, each port endincluding walls defining air andfuelpassages having relatively high heels, and other walls, includinglateral converging walls and a steep apron sloping uninterruptedlyupward from the hearth of the melting chamber to the lower side of thefuel passage and at an angle of above about 20 to a projection of saidfuel passage into said mixing chamber, arranged to direct air underneatha stream of fuel from said fuel passage and .to deflect said stream offuel downwardly into contact with the adjacent end of a. charge in saidmelting chamber.

10. An open hearth furnace including a melting chamber provided with aroof with knuckles at each end thereof disposed close to the lengthwisehorizontal plane of said roof, port ends at each end of the meltingchamber, air and fuel passages in each port end having relatively highheels, a mixing chamber connecting said passages in each port end withsaid melting chamber, wing Walls in each port end adjacent to a verticalplane thru the adjacent knuckle, a steep roof for each mixing chamber,and a step apron approximately parallel tosaid roof and sloping up fromthe melting chamber between the Wing walls to said air and fuelpassages, said roof making an included angle of more than about 20 withthe line of ow of fuel in the mixing chamber from said fuel passage.

11. An open hearth furnace including oppositely disposed port ends and amelting chamber therebetween, each port end includinga mixing chamberopening at one end into the melting chamber and air and fuel passageshaving relatively high heels disposed in substantially the samehorizontal plane and opening into the other end of said mixing chamber,the top surface of said gas and air passages making an included angle ofbetween about 20 and 4about 30, said mixing chamber having an apronsloping downwardly from the fuel passage at an angle of between about 30and about 50 to the horizontal, the area of said mixing chamberincreasing progressively from said passages to said melting chamber.

12. In an open hearth furnace, the combination in a port end thereof ofair and gas passages having relatively high heels, the projections ofsaid passages making an included angle of between about 20 and about 30,and a mixing chamber communicating with said passages at one end andincreasing in area therefrom to its opposite end, said mixing chamberhaving an apron sloping downwardly from the fuel passage at an angle ofbetween about 30 and about 50 to the horizontal.

GEORGE W. PUTNAM.

